Why Any Actuator Won't Do for Aerospace TestingMTS senior product manager Sterling Anderson describes the design and performance differences between industrial actuators and those engineered specifically for testing.
Q: Why do some test labs specify industrial actuators for aerospace testing?
Anderson: Many test labs are feeling cost pressures and want to save money. Others assume that all actuators are equal. With either of these mindsets, low purchase price becomes the primary motivation behind their buying decisions. Since actuators from manufacturers who serve other industries, such as mobile equipment, are available at a lower purchase price than those engineered for testing, these test labs simply go with the less expensive option.
It’s easy to assume that industrial and “test” actuators are equally suitable for static and dynamic testing. The two types of actuators look alike and appear to perform the same. But this is actually not the case.
Q: Why aren’t industrial actuators a suitable replacement those designed for testing?
Anderson: Industrial actuators are less reliable and energy-efficient than test actuators, and they’re not nearly as precise. This is due to a series of engineering innovations that clearly set test actuators apart from their industrial counterparts, including the fact that test actuators are fatigue-rated.
Industrial actuators are actually the more expensive option in the long run. Their purchase price may be lower, but their cost of ownership often far exceeds that of test actuators.
Q What do you mean by ‘fatigue-rated,’ and why is it so important?
Anderson: Simply stated, being fatigue-rated means that the actuator is designed to outlast the testing itself. Structural failure has been engineered out of the picture through a combination of elegant engineering, high-performance parts and quality manufacturing. This combination virtually eliminates the chance of structural failure, and yields actuators capable of enduring extreme numbers of cycles at intended loads throughout their expected life cycles.
For example, fatigue-rated MTS Series 201 actuators are designed to far exceed their rated load for millions of cycles. That means that structural failure will not occur when the actuator is operating at 100% of the rated load during a fatigue test.
In contrast, non-fatigue-rated actuators are designed to operate at 100% of the rated load, at best. This means that these actuators are operating at the very threshold of their load capacity under normal operating conditions. Manufacturers of these actuators use lower-quality parts and apply fewer engineering hours to keep their costs down, resulting in products far more prone to structural failure.
Industrial actuators may perform sufficiently at the beginning, but the heavy cycling required for test applications will lead to progressively degraded performance and possibly structural failure. Because such failures occur suddenly and with no prior warning, they can be very detrimental to productivity and also cause irreparable damage to multi-million-dollar test articles.
Q: How are you able to achieve such superior performance with MTS Series 201 actuators?
Anderson: Superior Series 201 performance results from the close attention we pay to design details. MTS Series 201 actuators include several subtle but critical engineering innovations that combine to enhance actuator reliability, energy-efficiency and precision.
First, they feature bolted connections between rods and pistons, which are far superior to the threaded connections employed by many industrial actuator suppliers to cut manufacturing costs. Threaded connections are a frequent cause of structural failure.
MTS actuators also integrate four fatigue-rated tie rods, one at each end cap corner, that are pre-loaded with torque exceeding the rated load of the actuator. This configuration creates the stiffness necessary to counter axial stresses and minimize the wearing effects of heavy cycling.
MTS actuators utilize high-performance polymer bearings, featuring relatively large surface areas. This design withstands high moments caused by cantilevering forces far better than the brass bearings typically used in industrial actuators. Additionally, polymer bearing wear is far less likely to cause hydraulic system degradation. Brass bearings slough off highly abrasive particles as they wear, contaminating hydraulic fluid and accelerating pump and manifold degradation. Over time, such degradation can lead to system control problems.
Low-friction seals are used in MTS actuators to provide ideal tolerance levels while introducing the minimum amount of friction into the system. Seal frictional characteristics for MTS Series 201 actuators are 1% of the rated load, compared to the 10% that is typical for industrial actuators. This means that a 3000psi industrial actuator requires 300psi of energy just to move the piston, while an MTS test actuator requires only 30 psi.
It’s easy to see the inefficiency here. With high frictional characteristics, industrial actuators often require additional pumping power to move the fluid. If the hydraulic power unit is located across the test lab, a bigger, more expensive distribution system may also be required to maintain the necessary pressures, due to fluid frictional losses.
MTS Series 201 actuators also include the same high-precision valves and transducers used with our top-of-the-line actuators. Such high-performance components will enable test labs to achieve the best possible control fidelity from their testing.
Q: How will test labs benefit from using test actuators instead of industrial actuators?
Anderson: It will give them absolute confidence in the reliability of their static and dynamic test setup. By using actuators designed specifically for testing, aerospace test labs will have a clear picture of how long the actuator will last and what loads it will withstand, across generations of tests.
Using test actuators will also help an aerospace test lab to optimize cost-efficiency. These actuators might have a slightly higher purchase price than industrial actuators, but this differential will easily be recovered through increased uptime and energy savings.
In addition, by choosing MTS as their test solutions partner, test labs can tap into an unmatched reservoir of system integration expertise. We not only offer test-level expertise, but can also help aerospace test programs create the most efficient overall system design possible.
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